CHICAGO — In a city and state known for tenacious corruption, U.S. Attorney Patrick Fitzgerald became known for equal tenacity in going after politicians of every stripe.

During more than a decade in Chicago, Fitzgerald put behind bars a former Republican governor and then his Democratic successor. He traveled to Washington to win convictions of a top aide to the vice president of the United States, and back home targeted an international media mogul and aides to one of the nation's most powerful mayors.

On Wednesday, two months after former Gov. Rod Blagojevich walked into prison following Fitzgerald's insistence he be tried a second time for trying to sell a Senate appointment, Fitzgerald announced he is stepping down after 24 years as a prosecutor.

Fitzgerald gave no reason for his decision to leave the presidentially appointed post he's held since Sept. 1, 2001. During that time he's overseen prosecutions of Blagojevich and former Gov. George Ryan, former Vice President Dick Cheney's top aide I. Lewis "Scooter" Libby and media mogul Conrad Black. He took on public corruption, international terrorism, corporate fraud and organized crime.

"Eleven years is a very long time in a very high-pressure job," said Peter Fitzgerald, a former U.S. senator, no relation, who recruited Patrick Fitzgerald to the post and spoke to him about his decision. "I think it's really hard ... to divide responsibilities between family and job. I think he just felt it was time and also thought the office would benefit from new blood."

Fitzgerald, who is married to a schoolteacher and has two young children, will hold a Thursday news conference but said in his statement that he wants take the summer off before considering other job possibilities.

"When I was selected for this position in 2001, I said that it was one of the greatest privileges that I could ever hope for," he said in the statement. "I believe that even more now after having the privilege of working alongside hundreds of dedicated prosecutors and agents."

Fitzgerald has been mentioned as a possible successor to FBI Director Robert Mueller. He has said he would never consider elected public office.

In fact, after being appointed by a Republican President George W. Bush and keeping his job under Democratic President Barack Obama, the intensely private prosecutor has never publicly made his politics known.

"He was one of the most non-political U.S. attorneys we've ever had ... and in a town like this where everything is political, it is incredible to have a U.S. attorney like that," said former state appellate Judge David Erickson.

Job prospects or no, the timing of Fitzgerald's announcement makes sense, coming just after his office saw through Blagojevich's imprisonment and the last major cases stemming from the yearslong investigation of the former governor.

It was that case that tested Fitzgerald like no other in Chicago.

From the day of Blagojevich's 2008 arrest, when Fitzgerald famously characterized the former governor's actions as a "political corruption crime spree" that would "make Lincoln roll over in his grave," he has been scrutinized for the case.

"I worked under three U.S. attorneys and none of them ever would have uttered such comments, and if any assistant did, he or she would have been fired immediately," said Phil Turner, who worked in the northern Illinois office before Fitzgerald's tenure began.

Criticism mounted when the jury in Blagojevich's first trial deadlocked on the vast majority of charges, including the most damaging allegation that he tried to sell Obama's vacant Senate seat to the highest bidder.

The Washington Post published a scathing editorial saying Fitzgerald had his shot and "should stand down before crossing another fine line – the one that separates prosecution from persecution." The Wall Street Journal called for his resignation or removal.

Undaunted, Fitzgerald tried Blagojevich again and secured a conviction that resulted in a 14-year prison term for the ex-governor.

While critics insist Fitzgerald crosses lines, attorneys in his office are intensely loyal.

"He's just a guy who does the right thing," said Joel Levin, who left the office after he helped prosecute Ryan. "He is a person of incredible integrity."

To those he targeted, Fitzgerald may be the country's most-feared federal prosecutor. In addition to the ex-governors, his office won convictions against aging mobsters, city workers, trucking executives and top figures in former Chicago Mayor Richard Daley's administration.

He was tapped as a special prosecutor to investigate the disclosure of CIA operative Valerie Plame's identity and eventually won the conviction against Libby, though Bush later commuted his sentence.

In that case, Fitzgerald tried to force former New York Times reporter Judith Miller to testify before a grand jury, with Miller sitting in jail for three months for refusing to do so. She ultimately relented, saying Libby had given her permission to publish Plame's name.

Born in Brooklyn, N.Y., the son of a Manhattan doorman, Fitzgerald spent years advancing his career one criminal case at a time. He earned a reputation as a tough anti-corruption prosecutor who worked, as one observer put it, "28 hours a day."

As an assistant U.S. attorney in New York he successfully prosecuted major terrorism cases, including against those responsible for the 1998 bombing of two U.S. embassies in East Africa and Omar Abdel-Rahman, the so-called "blind sheik," convicted of the 1993 World Trade Center bombing and conspiring to blow up bridges and buildings around New York.

In 1993, he helped jail a Gambino crime family capo and three other mobsters for murder, racketeering, narcotics trafficking and other crimes. And he supervised the 1996 trial of three men who plotted to blow up 12 airliners.

"From his early consequential years in New York City confronting the terrorist threat to his strong leadership of the U.S. Attorney's Office for the Northern District of Illinois, Pat has rightly earned a reputation over these last 24 years as a prosecutor's prosecutor," U.S. Attorney General Eric Holder said in a Wednesday statement.

Fitzgerald was among 10 or more people with strong credentials in law enforcement whose names were mentioned a year ago as possible nominees to succeed Mueller as his 10-year term leading the FBI neared an end. President Barack Obama decided to keep Mueller in place until September 2013.

During an appearance last week before the Senate Judiciary Committee, Mueller said he has had discussions with Obama about potential successors, but "not very recently."

If Fitzgerald were to accept a nomination, he could potentially run into opposition on Capitol Hill from Republicans, some of whom viewed Libby's prosecution as prosecutorial overreach.

"He's done and incredible job and ... most of us in this profession think the world's wide open for him," said Anton Valukas, who headed the U.S. attorney's office in Chicago from 1985-1990. "All the big firms in the country will want him to come to the private side and I would be surprised if he is not considered for a high political post."

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Associated Press writers Jason Keyser in Chicago and Pete Yost in Washington contributed to this report.

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